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Present work investigates the relationship between the combustion parameters of a well-known ECN heavy-duty nozzle called Spray D and marine-size nozzles. The study is carried out in OpenFOAM software within the framework of RANS turbulence modelling, using a flamelet based tabulation technique known as FGM to model the combustion. The large nozzles are tested in a constant volume chamber representative of marine engines, for which a CFD setup is validated against inert data in literature. The reacting results have been validated first with experimental data, initializing the domain with a highly reactive environment (23% oxygen) and engine-like swirl. Then, a less reactive initial condition was set up in the domain (15% oxygen) without swirl, to achieve a Spray D-like environment.

Bio-derived butanol is a potential CO2 neutral alternative fuel to be applied in internal combustion engines. However, the physical and combustion characteristics have to be fully understood before it can be used efficiently in engines. This work investigates the viscosity and the combustion characteristics of n-butanol/diesel fuel blends, with a particular focus on the combustion property at low load performance. N-butanol was mixed with diesel from 20 vol% up to 80 vol% blend ratio. Tests were performed in a combustion research unit (constant volume) at fixed chamber pressure that mimic a low load condition. The effects of various chamber temperatures and ambient oxygen concentrations (21%, 13%, and 11%) are evaluated. As expected, the viscosity of n-butanol/diesel fuel blends decreases at high temperature. The decrease is non-linear with the blend ratio.

Partially premixed combustion (PPC) is a low temperature combustion (LTC) concept which can relieve soot-NOx trade-off without sacrificing efficiency. However, at low load operating range, PPC with low reactivity fuel generally undergoes long ignition delay, which gives rise to high pressure rise rate, fast heat release and even misfires. To solve these problems and maintain high efficiency simultaneously, inlet heating, inlet boosting and double-injection strategy are experimentally investigated in a heavy-duty engine. BH80 (80vol% n-butanol and 20vol% n-heptane) are blended and tested at 8 bar gIMEP in PPC mode. Inlet heating (from 40oC to 100oC), inlet boosting (from 1.4 bar to 2.5 bar) and a double-injection strategy (pilot/main injection) are attempted to reduce the maximum pressure rise rate (PRRmax). The results show that all three methods can achieve negligible soot emissions. Moreover, a correlation between global temperature at TDC and ignition delay is noticed.

Low temperature combustion concepts are studied recently to simultaneously reduce NOX and soot emissions. Optical studies are performed to study gasoline PPC in CI engines to investigate in-cylinder combustion and stratification. It is imperative to perform emission measurements and interpret the results with combustion images. In this work, we attempt to investigate this during the transition from CI to HCCI mode for FACE I gasoline (RON = 70) and its surrogate, PRF70. The experiments are performed in a single cylinder optical engine that runs at a speed of 1200 rpm. Considering the safety of engine, testing was done at lower IMEP (3 bar) and combustion is visualized using a high-speed camera through a window in the bottom of the bowl. From the engine experiments, it is clear that intake air temperature requirement is different at various combustion modes to maintain the same combustion phasing.

Multiple-injection strategies are characterized by a complex and transient interplay between high- and low-temperature reactions. Tracking low-temperature reaction products such as formaldehyde (CH2O) is particularly important to understand ignition phenomena and the so-called “combustion recession” that is observed in experiments. Experimentally, it is often difficult to discriminate between formaldehyde and other species such as poly-aromatic hydrocarbons, which is why a selective excitation approach is used in this work. Simultaneous high-speed imaging of the chemically-excited hydroxyl radical (OH*) is used to improve indication of flame location and second stage ignition. During experiments in a constant-volume vessel, two 0.5-ms injections of n-dodecane, separated by 0.5-ms dwell time, are injected into a 900-K ambient.

This study demonstrates the combustion stratification from conventional compression ignition (CI) combustion to partially premixed combustion (PPC). Experiments are performed in an optical CI engine at a speed of 1200 rpm for diesel and naphtha (RON = 46). The motored pressure at TDC is maintained at 35 bar and fuelMEP is kept constant at 5.1 bar to account for the difference in fuel properties between naphtha and diesel. Single injection strategy is employed and the fuel is injected at a pressure of 800 bar. Photron FASTCAM SA4 that captures in-cylinder combustion at the rate of 10000 frames per second is employed. The captured high speed video is processed to study the combustion homogeneity based on an algorithm reported in previous studies. Starting from late fuel injection timings, combustion stratification is investigated by advancing the fuel injection timings. For late start of injection (SOI), a direct link between SOI and combustion phasing is noticed.

Partially Premixed Combustion (PPC) is a promising combustion concept ,based on judicious tuning of the charge stratification, to meet the increasing demands of emission legislation and to improve fuel efficiency. Longer ignition delays of PPC in comparison with conventional diesel combustion provide better fuel/air mixture which decreases soot and NOx emissions. Moreover, a proper injection timing and strategy for PPC can improve the combustion stability as a result of a higher level of fuel stratification in comparison with the Homogeneous Charge Compression Ignition (HCCI) concept. Injection timing is the major parameter with which to affect the level of fuel and combustion stratification and to control the combustion phasing and the heat release behavior. The scope of the present study is to investigate the fluid flow characteristics of PPC at different injection timings.